Contribution submitted via Github - fix CMySQLCursor.fetchmany
(*) Contribution by Bruce Feng (Github brucefeng10, mysql-connector-python/pull/54#issuecomment-559636345): I confirm the code being submitted is offered under the terms of the OCA, and that I am authorized to contribute it.

Posted by developer:
Fixed as of the upcoming MySQL Connector/Python 8.0.20 release, and here's the proposed changelog entry by the documentation team:
The fetchmany() method failed to function properly when the last fetch was
not a full batch; and would hang. Thanks to Bruce Feng for the patch.
Thank you for the bug report.